The Hagen Marina Submersible Glass Aquarium Heater 6 inch option is both compact and fully submersible. Available in both 25 and 50 Watts. The 25 Watt option is ideal for aquariums nano 3-5 Gallons, the 50 Watt option is ideal for small 5-10 Gallons. You can dial in the desired temperature on the top, and the heater will automatically regulate to maintain that temperature. It has a heating indicator lamp and is constructed with impact-resistant glass for safety. This heater is reliable for keeping your tropical fish tank at a steady warm temperature, preventing harmful temperature swings. Available in Multiple Wattage Options